5.10-stable review patch. If anyone has any objections, please let me know.
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From: Valentin Schneider valentin.schneider@arm.com
[ Upstream commit efd984c481abb516fab8bafb25bf41fd9397a43c ]
A following patch will trigger NOHZ idle balances as a means to update nohz.next_balance. Vincent noted that blocked load updates can have non-negligible overhead, which should be avoided if the intent is to only update nohz.next_balance.
Add a new NOHZ balance kick flag, NOHZ_NEXT_KICK. Gate NOHZ blocked load update by the presence of NOHZ_STATS_KICK - currently all NOHZ balance kicks will have the NOHZ_STATS_KICK flag set, so no change in behaviour is expected.
Suggested-by: Vincent Guittot vincent.guittot@linaro.org Signed-off-by: Valentin Schneider valentin.schneider@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Vincent Guittot vincent.guittot@linaro.org Link: https://lkml.kernel.org/r/20210823111700.2842997-2-valentin.schneider@arm.co... Stable-dep-of: ff47a0acfcce ("sched/fair: Check idle_cpu() before need_resched() to detect ilb CPU turning busy") Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/fair.c | 24 ++++++++++++++---------- kernel/sched/sched.h | 8 +++++++- 2 files changed, 21 insertions(+), 11 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8121cfd60b8fb..e2116e3d593ec 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10438,7 +10438,7 @@ static void nohz_balancer_kick(struct rq *rq) goto out;
if (rq->nr_running >= 2) { - flags = NOHZ_KICK_MASK; + flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK; goto out; }
@@ -10452,7 +10452,7 @@ static void nohz_balancer_kick(struct rq *rq) * on. */ if (rq->cfs.h_nr_running >= 1 && check_cpu_capacity(rq, sd)) { - flags = NOHZ_KICK_MASK; + flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK; goto unlock; } } @@ -10466,7 +10466,7 @@ static void nohz_balancer_kick(struct rq *rq) */ for_each_cpu_and(i, sched_domain_span(sd), nohz.idle_cpus_mask) { if (sched_asym_prefer(i, cpu)) { - flags = NOHZ_KICK_MASK; + flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK; goto unlock; } } @@ -10479,7 +10479,7 @@ static void nohz_balancer_kick(struct rq *rq) * to run the misfit task on. */ if (check_misfit_status(rq, sd)) { - flags = NOHZ_KICK_MASK; + flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK; goto unlock; }
@@ -10506,7 +10506,7 @@ static void nohz_balancer_kick(struct rq *rq) */ nr_busy = atomic_read(&sds->nr_busy_cpus); if (nr_busy > 1) { - flags = NOHZ_KICK_MASK; + flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK; goto unlock; } } @@ -10653,7 +10653,8 @@ static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags, * setting the flag, we are sure to not clear the state and not * check the load of an idle cpu. */ - WRITE_ONCE(nohz.has_blocked, 0); + if (flags & NOHZ_STATS_KICK) + WRITE_ONCE(nohz.has_blocked, 0);
/* * Ensures that if we miss the CPU, we must see the has_blocked @@ -10675,13 +10676,15 @@ static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags, * balancing owner will pick it up. */ if (need_resched()) { - has_blocked_load = true; + if (flags & NOHZ_STATS_KICK) + has_blocked_load = true; goto abort; }
rq = cpu_rq(balance_cpu);
- has_blocked_load |= update_nohz_stats(rq); + if (flags & NOHZ_STATS_KICK) + has_blocked_load |= update_nohz_stats(rq);
/* * If time for next balance is due, @@ -10712,8 +10715,9 @@ static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags, if (likely(update_next_balance)) nohz.next_balance = next_balance;
- WRITE_ONCE(nohz.next_blocked, - now + msecs_to_jiffies(LOAD_AVG_PERIOD)); + if (flags & NOHZ_STATS_KICK) + WRITE_ONCE(nohz.next_blocked, + now + msecs_to_jiffies(LOAD_AVG_PERIOD));
/* The full idle balance loop has been done */ ret = true; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 66e3ecb7c10e4..5f17507bd66b8 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2293,12 +2293,18 @@ extern void cfs_bandwidth_usage_dec(void); #define NOHZ_BALANCE_KICK_BIT 0 #define NOHZ_STATS_KICK_BIT 1 #define NOHZ_NEWILB_KICK_BIT 2 +#define NOHZ_NEXT_KICK_BIT 3
+/* Run rebalance_domains() */ #define NOHZ_BALANCE_KICK BIT(NOHZ_BALANCE_KICK_BIT) +/* Update blocked load */ #define NOHZ_STATS_KICK BIT(NOHZ_STATS_KICK_BIT) +/* Update blocked load when entering idle */ #define NOHZ_NEWILB_KICK BIT(NOHZ_NEWILB_KICK_BIT) +/* Update nohz.next_balance */ +#define NOHZ_NEXT_KICK BIT(NOHZ_NEXT_KICK_BIT)
-#define NOHZ_KICK_MASK (NOHZ_BALANCE_KICK | NOHZ_STATS_KICK) +#define NOHZ_KICK_MASK (NOHZ_BALANCE_KICK | NOHZ_STATS_KICK | NOHZ_NEXT_KICK)
#define nohz_flags(cpu) (&cpu_rq(cpu)->nohz_flags)